An optical attenuator is an optical device that can modulate the power level of an optical signal. Based on the macro-bending loss of optical fibers, we present a wavy fiber attenuator where the attenuation level can be controlled by a mechanical-induced buckling of the fiber. By bonding a fiber to a prestretched substrate and then releasing the prestrain, the fiber flexes into a sinusoidal wavy curve due to the constraints of the substrate. The level of the light attenuation can simply be controlled by stretching the substrate. The maximum attenuation of the proposed wavy optical fiber attenuator is -87.3 dB.